Method of forming moulded printing negatives and positives



July 17, 1956 J w M5 2,754,606

METHOD OF FORMING MOULDED PRINTING NEGATIVES AND POSITIVES Filed May 4, 1950 4 Sheets-Sheet 2 IN VEN TOR.

July 17, 1956 J. WILLIAMS 2,754,606

METHOD OF FORMING MOULDED PRINTING NEGATIVES AND POSITIVES 4 Sheets-Sheet 3 Filed May 4, 1950 INVENTORJ a WM. 399% ATTORNEYS.

July 17, 1956 1 J. WILLIAMS 2,754,606

METHOD OF FORMING MOULDED PRINTING NEGATIVES AND POSITIVES Filed May 4, 1950 4 Sheets-Sheet 4 ,ZZQZZ LJ'LL' IN VEN TOR.

ATTORNEYS.

United States Patent NIETHOD OF FORMING MOULDED PRINTING NEGATIV ES AND POSITIVES John Williams, Chicago, Ill.

Application May 4, 1950, Serial No. 160,049

Claims. (Cl. 41-46) This invention relates to the production of negatives and positives utilized in forming roto and offset printing plates and is an improvement over the invention disclosed in my prior Patent No. 1,939,749, granted December 19, 1933.

The method disclosed in my prior patent for producing a negative for use in the production of offset printing plates comprises producing an etched plate of the matter to be printed, producing by impressions from said etched plate a reverse impression upon a hard nonmetallic plate such as Bakelite to form a die plate, producing by impression from said die plate an impression upon a transparent plate or sheet such as Celluloid,

which impression is the reverse of the die plate and a positive of the etched plate, and rendering the depressed portions of the transparent plate opaque to form a negative from which a print may be obtained upon the printing surface of an offset printing plate.

The manner of producing negatives and positives in accordance with this invention is basically like that of my aforementioned prior patent but includes certain definite improvements for providing improved results and greater adaptability.

The principal object of this invention is to provide an improved manner of producing negatives and positives wherein special or conventional routed or beveled master or etched letter press printing plates or combination, half-tone, line and type plates may be used, wherein the negatives accurately correspond to the original etched plates, wherein distortion is kept to a minimum, wherein accurate register is provided in the case of color printing and wherein the negatives may be rapidly and inexpensively made.

In accordance with this invention various types of etched metallic plates may be used in the production of the negative. Such etched metallic plates are oftentimes referred to as four color process plates, copper half-tones, cuts, photoengraving plates, half-tone plates, copper plates, relief plates, nickel-type, electrotype, and the like. The etched plate may be made especially for this purpose and in so doing is not carried as far as for letter press printing plates. All routing and beveling when necessary are kept very shallow. All dead metal and bearers should be left on the copper plate. In a combination plate the line or type work should not have more than a two bite deep etch depth. Such an engraving plate is ideal. An etched master plate which has been routed or beveled may also be used, and in accordance with this invention the routed or beveled portions may be temporarily filled. A square half-tone letter press plate where dead metal or bearers have been removed may also be used and here it is preferable to provide the same with additional strips of metal to act as bearers to improve the resulting impression on the negative and provide exensions for ease in handling the negative.

This invention also contemplates an improved block upon which a reverse impression is made by the etched may be reproduced in four colors.

'ice

metallic plate to form the die plate from which the negative is made. The improved block of this invention is so constructed that it is substantially unaffected by heat and pressure whereby distortion is kept to a minimum and color register is assured. In this connection the block includes a substantially rigid core which is substantially unaffected by heat and pressure. Applied to each side of the core is a partially cured thermosetting layer upon which an impression may be made by the etched metallic plate. When the etched metallic plate is placed against the block and heat and pressure are applied thereto, a reverse impression is moulded on the thermosetting layer and the thermosetting layer is completely cured thereby providing an accurate, firm and hard die plate. Distortion of the die plate due to heat and pressure is substantially eliminated by the substantially rigid core.

In producing the negative a thin transparent thermoplastic sheet is placed against the die plate and is backed up by a highly polished metallic plate. Pressure is applied and heat is also applied through the die plate whereby the die plate moulds a reverse impression (positive to the etched metallic plate) on the transparent thermoplastic sheet. The depressed portions of the trans parent thermoplastic sheet are then rendered opaque to form the negative from which negative contact positives are made and utilized for making offset and roto printing plates. The original metallic plates, from which the printing negatives of this invention are formed, may be used for different methods of printing, roto and offset. The process of this invention has definite advantages and produces great savings. It eliminates the necessity for deep routing, deep beveling, blocking or mounting, make-ready, electrotypes and nickeltypes. The original plates or ideal plates made especially for this process may be made from thinner gauge copper. Any subject Labor cost is greatly reduced and faster printing on cheaper paper is made possible. One-set of master plates will serve three kinds of printing, namely, letter press, roto and offset.

Other objects and advantages of this invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawings in which:

Fig. l-A is a perspective view of a metallic plate which is ideal for the purpose of this invention.

Fig. l-B is a perspective view of a metallic plate which has shallow routing and beveling, and which is also ideal for the purpose of this invention.

Fig. l is a perspective view of a routed or beveled etched metallic master plate;

Fig. 2 is a perspective view of a square half-tone etched metallic letter press printing plate with bearers removed;

Fig. 3 is a sectional view through the letter press printing plate of Fig. 2 with additional strips of metal to act as bearers associated therewith;

Fig. 4 is a sectional view through the etched master plate of Fig. l with a thin metallic sheet applied thereto which is utilized in the process of filling the routed or beveled portions;

Fig. 5 is a view similar to Fig. 4 but with the thin metallic sheet removed;

Fig. 6 is a view showing the manner of forming a laminated substantially rigid flat core;

Fig. 7 is a view of the manner of applying a layer of thermosetting material to each side of the core of Fig. 6;

Fig. 8 is a view similar to Fig. 7 but utilizing a core of fiber board;

Fig. 9 is a view similar to Fig. 7 but utilizing a core of metal;

Fig. 10 is a partial view of a heated press for forming 32 a block having a substantially rigid core and a thermosetting layer on each side of the core;

Fig. 11 is a partial view of a heated press showing the manner of transferring and molding the impression from the etched metallic plate onto the block for forming a die plate;

Fig. 12 is a perspective view of a die plate formed in the manner illustratedv in Fig. 11;

Fig. 13 is a partial view of a heated press illustrating the manner in which the impression on the die plate is transferred and molded to a transparent thermoplastic plate for forming a printing negative.

Fig. 14 is a perspective view of the negative formed in the manner illustrated in Fig. 13.

Various types of etched metallic plates may be used for the production of the negatives in accordance with this invention. As shown in Figure 1A an etched copper plate generally designated at 6 may be made especially for the purpose of this invention and it may include a copper plate 11 having an etched design 12 which may be squared or finished with a draw hook or other suitable tool. All the dead metal 14 is left on the plate and the dead metal around the design forms bearers. This copper plate preferably is not routedor beveled and in the case of a combination-plate all line or type Work should not have more than substantially a one or two bite depth. If routing or beveling is necessary, the same is made very shallow, not to exceed substantially a two bite deep etched depth in line and type work. Such a copper plate is generally designated at 7 in Figure 1B and it may include a copper plate 11 having an etched design 12 with all the dead metal 14 left thereon to form bearers. The routing 8 and the beveling 9 are made very shallow. Such plates are ideal for the purpose of this invention.

However, in usual letter press printing various types of plates are used, such as an etched master plate as designated generally at 10 in Fig. 1 which has beenrouted or beveled, and a square half-tone etched letter press plate as designated generally at in Fig. 2 in which the bearers have been removed. The routed or beveled etched metallic master plate 10 of Fig. 1 includes a metallic plate 11, usually a copper plate, which has a suitable design 12 etched on the surface thereof. The perimeter of the design 12 is routed or beveled at 13 and beyond the routed or beveled portion there remains dead metal 14 acting as bearers. Such a plate 10 is considered a master plate and is ordinarily utilized in making other plates such as nickle-types or electrotypes for printing purposes. The letter press printing plate 15 of Fig. 2 is a square half-tone and is essentially the same as the master plate 10 of Fig. l with the exception that the dead metal or bearers 14- have been removed. The letter press plate 15 may be utilized directly for letter press printing.

When the letter press plate 15 is utilized in accordance with this invention for forming a printing negative, it is preferably provided with additional metal to form bearers as illustrated in Fig. 3. In this connection metallic pieces 16 are placed along the edges of the letter press plate 15. In this way bearers are added so as to provide more uniform pressure when the letter press plate is placed in a hydraulic press and also to provide the resulting printing negative with additional material by which the negative may be handled without smearing the impression thereon.

When the etched master plate of Fig. l is utilized for the purpose of forming the printing negative, it is desirable to fill in the routed or beveled portions 13. To accomplish this a thin ductile metallic sheet, suchas a thin brass sheet, 18 is forced into the routed or beveled portions 13 as illustrated in Fig. 4. This may be accomplished by placing the etched plate 10 and the thin sheet 18 on a press with a rubber mat overlying the thin sheet. When pressure is applied the rubber mat forces the thin sheet into the routed or beveled portions 13 as.

illustrated at 19. The top of the thin sheet 18 is then preferably lubricated with graphite and oil and then a quick-hardening material, such as a quick-setting cement, is spread over the top of the lubricated thin sheet 18. This material fills in the depressions 19 in the thin sheet and the excess material is wiped clean from the thin sheet before hardening. The material then hardens in the depressions 19 and is illustrated at 20 in Fig. 4. After the material has hardened, it is lubricated, then the thin sheet 18 is removed from the master plate 10 and the hardened material 20 is transferred from the depressions 19 in the thin sheet into the routed or beveled portion 13 of the master plate 10 as illustrated in Fig. 5. In this way the depth of the routed or beveled portions 13 is filled. So-called combination plates are preferably treated in the same manner as the routed or beveled plates for filling the depth of the depressions therein. The etched plates treated in the foregoing manner are utilized for moulding a reverse impression on thermosetting blocks for forming die plates.

The thermosetting blocks and the manner of forming the same are illustrated in Figs. 6 to 10. Basically, they include a substantially rigid fiat core which is substantially unaffected by heat and pressure and a layer of partially cured thermosetting material on each side of the core. The thermosetting material may be any thermosetting plastic which hardens with the application of heat and pressure such as phenol formaldehyde commonly known as Bakelite. Fig. 6 illustrates one manner of forming a substantially rigid fiat core generally designated at 25. The core 25 is a laminated construction. For example, it may comprise three sheets of kraft paper 26 impregnated with a laminating thermo- On each setting resin such as phenol formaldehyde. side of these three sheets 26, is placed a sheet 27 of kraft paper impregnated with and having a high concentration of a similar thermosetting resin and preferably the resin is oil modified. Over each sheet 27 is placed a sheet 28 of plain kraft paper. A metal sheet is then placed on both sides and this laminated stack is then placed in a heated hydraulic press and is pressed and heated until the laminating resin is completely cured. The laminating thermosetting resin bonds together the various sheets of kraft paper to form an extremely rigid core construction which is substantially unaffected by further applications of heat and pressure. The high concentration of oil modified laminating resin in the sheets 27 operates firmly to bond the plain paper sheets 28 in place.

To form the thermosetting block, a sheet of thin kraft paper 29 known as surface paper) is applied to each side of the core 25, the paper being impregnated with a thermosetting laminating resin of high concentration and which is preferably oil modified. Two sheets of kraft paper 30 impregnated with thermosetting laminating resin are placed over the paper sheets 29. This stack is then placed in a heated press as illustrated in Fig. 10. The heated press includes a bed 35 and a head 36 which are suitably heated by steam passages 37 located therein. A polished metallic plate 38 is placed on each side of the stack when it is inserted in the press. Pressure and heat are applied and the thermosetting laminating resin is partially cured. The impregnated paper sheets 29 and 30 are bonded together and to the core 25' by the action of the heat and the pressure. The polished metal plates 38 operate to pie-surface the resulting block 40. Before the stack is placed in the press between the plates 33, the outer surfaces thereof are preferably covered with a thermosetting powder to insure a smooth resulting surface. After partial curing, the block 40 is cooled in the press by running cooling water through the passages 37. Thus, there is provided on each side of the substantially rigid core 25 a partially cured thermosetting layer having an extremely smooth outer surface.

Figure 8 illustrates a block generally designatedat 41 which is like the block of Fig. 7 except that a different core is utilized. The block 41 of Fig. 8 uses a core 32 made out of fiber board which'has previously been compressed and hardened. The manner of making the block 41 of Fig. 8 is substantially the same as making the block 40 of Fig. 7. In Fig. 9 the core 33 is made of a sheet of metal and has the thermosetting layers applied to each side thereof. In this form of block the highly concentrated thermosetting laminating resin of the sheets 29 preferably contain no oil so that it will bond more securely to the metal core 33.

While the partially curved thermosetting layers on each side of the core have been illustrated as being formed from a laminated construction, of course these layers may be formed directly without laminations as by applying thermosetting material such as powder directly to each side of the core and then partially curing the same in a heated press. The block formed in accordance with this invention presents outer partially cured thermosetting surfaces which may be readily moulded by heat and pressure and at the same time includes a substantially rigid core for supporting these surfaces so that distortion of the block is substantially prevented when heat and pressure are subsequently applied thereto.

In accordance with this invention the etched metallic plates are utilized for moulding reverse impressions on the thermosetting blocks for producing die plates, which in turn are utilized for forming the negatives. In this connection a heated press is utilized as illustrated in Fig. 11. The heated press consists of a bed 45 and a head 46 which are heated by steam passages 47 therein. Preferably, a number of blocks are formed into die plates in one operation, especially where the resulting die plates are related for producing negatives for color printing. This is desirable where accurate register of color is required. This insures accurate register of color. Fig. 11, by way of illustration, shows two blocks being formed into die plates at the same time, wherein there is placed between the bed 45 and head 46 a stack consisting of an etched metallic plate 10, a block 40, a polished metallic plate 48, a heavy metallic plate 49, a polished metallic plate 48, a block 40, and an etched plate 10. A thin sheet of metal may be placed on top of the stack. When the stack is being prepared, the etched surfaces of the etched metallic plates are lubricated with a suitable lubricant, such as graphite and oil, to prevent the blocks from sticking thereto. Pressure and heat are applied by the press to the stack until the thermosetting layers of the blocks are substantially completely cured so that the reverse impressions moulded in the thermosetting layers are accurate, firm and permanent. Thus a hard die plate is produced. The substantially rigid core prevents distortion of the die plate during and after the moulding of the reverse impression thereon. The die plate is preferably cooled in the press by circulating water through the passages 47.

A die plate thus formed in the manner illustrated in Fig. 11 is generally designated at 50 in Fig. 12. It includes the block 40 having a reverse impression 51 thereon. It will also have additional material 52 corresponding to the portions 20 and 14 of the etched metallic plate as illustrated in Fig. 5. This additional material may be utilized for handling the die plate 50 without impairing the reverse impression 51 thereon.

Instead of forming the die plate 50 from the prepared block 40 it may also be formed directly from the core and thermosetting layers without the intermediate step of forming the block. In this respect a thermosetting layer, such as the one including impregnated paper sheets 29 and 30, may be placed on each side of the cores 2532-33 as illustrated in Figs. 7, 8 and 9. The outer surfaces of the thermosetting layers may then be covered with a thermosetting powder. This laminated structure may then be placed in a heated press along with the etched plates in the manner illustrated in Fig. 11 and heated and pressed until the thermosetting layers are completely cured. In this way the reverse impression may be moulded into the thermosetting layer at the same time that the thermosetting layer is being bonded to the core and being cured. The etched plates are suitably lubricated so that the thermosetting layers will not stick thereto.

The hard die plate 50 thus formed is utilized for forming the printing negative and this may be accomplished in a heated press as illustrated in Fig. 13. Here again it is desirable to form a plurality of printing negatives from a plurality of die plates in a single operation. The heated press may include a bed 55 and a head 56 heated by steam passages 57 therein. Between the bed and head is placed a stack consisting of a resilient fiber pad which may include a flannel pad or blanket 58 and a couple of layers of soft paper 59, a die plate 50 and a thin sheet of transparent thermoplastic material 60 such as Celluloid or paralin or the like. Over the transparent thermoplastic sheet 60 is placed a highly polished metallic plate 61 and a heavy metallic plate 62. The stack also includes like elements in reverse between the heavy plate 62 and the head 56. A thin sheet of metal may be placed on the top of the stack. When pressure is applied to the stack by the press and heat is applied to the thin thermoplastic sheets 60, the thermosetting die plate moulds a reverse impression (positive to the etched plate) in the thin transparent thermoplastic sheet 60. The highly polished metallic plate 61, by presenting an extremely smooth backing for the transparent thermoplastic sheets during moulding of the same by the die plates, maintain the thermoplastic sheets in a transparent condition. The resilient fiber pad operates to provide even pressure between the thermosetting die plate and the transparent thermoplastic sheet so that a faithful reproduction is obtained. The heat from the press that heats the transparent thermoplastic sheets 60 passes through the resilient fiber pads including the blankets and paper and the thermosetting die plates and in this way the heat is uniformly applied to the thin transparent thermoplastic sheets 60. The blankets 58 also operate to keep the cold air from contacting the transparent thermoplastic sheets. This also prevents burning or discoloring of the transparent thermoplastic sheets 60. The stack is preferably cooled under pressure by circulating water through the passages 57.

The transparent thermoplastic sheet with the impression moulded thereon in the manner illustrated in Fig. 13 forms a printing negative as is generally designated at 65 in Fig. 14. It includes the thin transparent thermoplastic sheet 60 having an impression 66 formed thereon, which impression is positive with respect to the design of the original etched plate. It also includes additional material 67 corresponding to the additional material 52 of the die plate of Fig. 12. This additional material provides for ready handling of the negative 65. The depressed portions of the transparent thermoplastic sheet are then rendered opaque. This may be accomplished by covering the impression thereon with printing ink, enamel or the like, and then rubbed with lamp black to create a greater density and also aid in rapid drying. The sheet is then quickly wiped oif. Thus the raised portions of the impression are cleaned while the depressed portions are rendered opaque. In rendering opaque the depressed portions it is preferable to perform this operation over a lighted bench, i. e. a bench with a translucent glass surface with a light below the same. All dead metal and parts not wanted to print are opaqued on the negatives. The resulting negative 65, thus mechanically formed, corresponds to a photographic negative from which an offset albumin printing plate may be made. If the job should be printed in the deep etch method or if a roto printing plate is required, a contact positive may be made from this negative which positive is suited for both types of printing.

While for. purposes of illustration one form of this invention has been disclosed, other forms thereof may become apparent to those skilled in the art and, accordingly, this .invention is tobe limited only by the scope of the appended claims.

I claim:

I. The method of forming thin printing negatives, which consists of, forming a block having a substantially rigid core which is substantially unaffected by heat and pressure applied thereto during subsequent molding operations and having a partially cured layer of thermo setting material on each side of the core, forming a metallic plate with desired shallow depressions wherein the depressions do not exceed a depth corresponding substantially to a two bite deep etched depth, lubricating said metallic plate and applying the same against one of the thermosetting layers, subjecting said metallic plate, thermosetting layers and core to heat and pressure for pressing the metallic plate against the thermosetting layer for molding shallow reverse impressions therein and for substantially completely curing the thermosetting layers to provide a hard die plate, sandwiching a thin transparent thermoplastic sheet between a highly polished miltallic plate and the hard die plate, applying pressure to the stack and heat through the die plate for molding shallow positive impressions in the thin transparent thermoplastic sheet, and rendering portions of the thin transparent thermoplastic sheet, including the shallow depressions thereof, opaque.

2. In a method of forming thin printing negatives, the steps comprising, forming a block having a substantially rigid core which is substantially unaflected by heat and pressure applied thereto during subsequent moldin operations and having a partially cured layer of thermosetting material on each side of the core, forming a metallic plate with desired shallow depressions wherein the depressions do not exceed a depth corresponding substantially to a two bite deep etched depth, lubricating said metallic plate and applying the same against one of the thermosetting layers, subjecting said metallic plate, thermosetting layers and core to heat and pressure for pressing the metallic plate against the thermosetting layer for molding shallow reverse impressions therein and for substantially completely curing the thermosetting layers to provide a hard die plate, sandwiching a thin transparent thermoplastic sheet between a highly polished metallic plate and a hard die plate, applying pressure to the stack and heat through the die plate for molding shallow positive impressions in the thin transparent thermoplastic sheet.

3. The method of forming a hard die plate for the purpose of molding thin printing negatives, which consists of, forming a block having a substantially rigid core which is substantially unaffected by heat and pressure applied thereto during subsequent molding operations and having a partially cured layer of thermosetting material on each side of the core, forming a metallic plate with desired shallow depressions wherein the depressions do not exceed a depth corresponding substantially to a two bite deep etched depth, lubricating said metallic plate and applying the same against one of the thermosetting layers, subjecting said metallic plate, thermosetting layers and core to heat and pressure for pressing the metallic plate against the thermo-setting layer for molding shallow reverse impressions therein and for substantially completely curing the thermosetting layers.

4. The method of forming thin printing positives for use in the production of roto printing cylinders and deep etch offset printing plates, which consists of, forming a block having a substantially rigid core which is substantially unafiectcd by heat and pressure applied thereto during subsequent molding operations and having a partially cured layer of thermosetting material on each side of the core, forming a metallic. plate with desired shallow depressions wherein the depressions do not exceed a depth,

corresponding substantially to a two bite deep etched depth, lubricating said metallic plate and applying the same against one of the thermosetting layers, subjecting said metallic plate, thermosetting layers and core to heat and pressure for pressing the metallic plate against the thermosett'ing layer for molding shallow reverse impressions therein and for substantially completely curing the thermosetting layers to provide a hard die plate, sand wi'ching a thin transparent thermoplastic sheet between a highly polished metallic plate and the hard die plate, applying pressure to the stack and heat through the die plate for moldingi shallow positive impressions in the thin transparent thermoplastic sheet, and. rendering portions of the thin transparent thermoplastic sheet, including the shallow depressions thereof, opaque to form a thin printing negatwo.

5. The method of forming a hard die plate for the purpose of molding thin printing negatives, which consists of, forming a substantially rigid fiat core which is substantially unaffected by heat and pressure applied thereto during subsequent molding operations, applying a layer of thermosetting material including therm0setting powder to each side of the core, forming a metallic plate with desired shallow depressions wherein the depressions do not exceed a depth corresponding substantially to a two bite deep etched depth, lubricating said metallic plate and applying the same against one of the thermosctting layers, subjecting said metallic plate, thermosetting layers and core to heat and pressure for pressing the metallic plate against the thermosetting layer for molding shallow reverse impressions therein and for substantially completely curing the thermosetting layers.

6. The method of forming a hard die plate for the purpose of molding thin printing negatives, which consists of, forming a substantially rigid flat core which is substantially unaflfected by heat and pressure applied thereto during subsequent molding operations, applying a layer of thermosettin'g material to each side of the core, placing a polished and lubricated metal plate on the outside of each thermosetting layer, subjecting the metal plates, thermosetting layers and core to heat and pressure for bonding the thermosetting layers to the core and for partially curing and pre-surfacing the thermosetting layers, forming a metallic plate with desired shallow depressions wherein the depressions do not exceed a depth corresponding substantially to a two bite deep etched depth, lubricating said metallic plate and applying the same against one of the thermosetting layers, subjecting said metallic plate, thermosetting layers and core to heat and pressure for pressing the metallic plate against the thermosetting layer for molding shallow reverse impressions therein and for substantially completely curing the thermosetting layers.

7. In the method of forming thin printing negatives, the steps comprising, forming a hard die plate having a substantially rigid core which is substantially unaffected by heat and pressure applied thereto during molding operations, having hard thermosetting layers on each side of the core, and having shallow depressions in one of the thermosetting layers which do not exceed a depth corresponding substantially to a two bite deep etched depth, sandwiching a thin transparent thermoplastic sheet between a highly polished metallic plate and the thermosetting layer of the hard die plate having the shallow depressions therein, and applying pressure to the stack and heat through the die plate for molding shallow impressions in the thin thermoplastic sheet.

8. In the method of forming thin printing negatives, the steps comprising, forming a plurality of hard die plates, each having a substantially rigid core which is substantially unaffected by heat and pressure applied thereto during molding operations, having hard thermosetting layers on each side of the core, and having shallow depressions in; one of the thermosetting layerswhich' do not exceed a depth corresponding substantially to a two 9. bite deep etched depth, stacking in the order named, a resilient fiber pad, a hard die plate, a thin transparent thermoplastic sheet, a highly polished metal plate, a metallic backing plate, a highly polished metal plate, a thin transparent thermoplastic sheet, a hard die plate, and a resilient fiber pad, the shallow depressions in the hard die plates engaging the thin transparent thermoplastic sheets, and applying pressure to the stack and heat through the fiber pads and die plates for molding shallow impressions in the thin thermoplastic sheets.

9. In the method of forming hard die plates for the purpose of molding thin printing negatives, which consists of, forming a plurality of blocks each having a substantially rigid core which is substantially unalfected by heat and pressure applied thereto during subsequent molding operations and having a partially cured layer of therrnosetting material on each side of the core, forming a plurality of metallic plates, each with desired depressions wherein the desired depressions do not exceed a depth coresponding substantially to a two bite deep etched depth, stacking in the order named, a lubricated metallic plate, a block, a polished metal plate, a metal backing plate, a polished metal plate, a block, and a lubricated metallic plate, the shallow depressions in the metallic plates engaging the blocks, and applying pressure to the stack and heat through the metallic plates for pressing the metalic plates against the therrnosetting layers of the blocks for molding shallow impressions therein and for substantially completely curing the therrnosetting layers.

10. In the method of forming thin printing negatives, the steps comprising, forming a plurality of blocks each having a substantially rigid core which is substantially unaflected by heat and pressure applied thereto during subsequent molding operations and having a partially cured layer of therrnosetting material on each side of the core, forming a plurality of metallic plates, each with desired depressions wherein the desired depressions do not exceed a depth corresponding substantially to a two bite deep etched depth, stacking in the order named, a lubricated metallic plate, a block, a polished metal plate, a metal backing plate, a polished metal plate, a block, and a lubricated metallic plate, the shallow depressions in the metallic plates engaging the blocks, and applying pressure to the stack and heat through the metallic plates for pressing the metallic plates against the therrnosetting layers of the blocks for molding shallow impressions therein and for substantially completely curing the thermosetting layers to form a plurality of hard die plates, stacking, in the order named, a resilient fiber pad, a hard die plate, a thin transparent thermoplastic sheet, a highly polished metal plate, a metallic backing plate, a highly polished metal plate, a thin transparent thermoplastic sheet, a hard die plate, and a resilient fiber pad, the shallow depressions in the hard die plate engaging the thin transparent thermoplastic sheets, and applying pressure to the stack and heat through the fiber pads and die plates for molding shallow impressions in the thin thermoplastic sheets.

References Cited in the file of this patent UNITED STATES PATENTS 1,398,142 Novotny Nov. 22, 1921 1,601,287 Bertinetti Sept. 28, 1926 1,673,239 Groff June 12, 1928 1,880,930 Elbel et a1. Oct. 4, 1932 1,939,749 Williams Dec. 19, 1933 1,973,548 Swan et al. Sept. 11, 1934 2,028,712 Swan et al. Jan. 21, 1936 2,139,054 Wilson Dec. 6, 1938 2,227,139 Kelly et a1. Dec. 31, 1940 2,303,395 Schultz et al. Dec. 1, 1942 2,383,567 Rudnick Aug. 28, 1945 

7. IN THE METHOD OF FORMING THIN PRINTING NEGATIVES THE STEPS COMPRISING, FORMING A HARD DIE PLATE HAVING A SUBSTANTIALLY RIGID CORE WHICH IS SUBSTANTIALLY UNAFFECTED BY HEAT AND PRESSURE APPLIED THERETO DURING MOLDING OPERATIONS, HAVING HARD THERMOSETTING LAYERS ON EACH SIDE OF THE CORE, AND HAVING SHALLOW DEPRESSIONS IN ONE OF THE THERMOSETTING LAYERS WHICH DO NOT EXCEED A DEPTH CORRESPONDING SUBSTANTIALLY TO A TWO BITE DEEP ETCHED DEPTH, SANDWICHING A THIN TRANSPARENT THERMOPLASTIC SHEET BETWEEN A HIGHLY POLISHED METALLIC PLATE AND THE TERMOSETTING LAYER OF THE HARD DIE PLATE HAVING THE SHALLOW DEPRESSIONS THEREIN, AND APPLYING PRESSURE TO THE STACK AND HEAT THROUGH THE DIE PLATE FOR MOLDING SHALLOW IMPRESSIONS IN THE THIN THERMOPLASTIC SHEET. 